186 On the Physical Properties of Soil 



size^*^' furnished at its four corners with steel points rounded off 

 below, and placed on a layer of soil three inches deep; the weights 

 placed on the plate, which are required in order to force it into 

 the soil, serve as the measure of this consistence : in the case, 

 however^ of stiff soils in a dry state, this method is attended with 

 the inconvenience and difficulty of requiring very great weights to 

 be laid upon the plate : with pure clay even 30 pounds are not 

 sufficient for the pm'pose ; while, in the case of very loose earth, 

 the plate sinks too easily. In order to obviate these difficulties, 

 Meyer proposes to submit the earths to this trial with an equal 

 measure (5 per cent.) of water in each — a modification, however, 

 which, in the execution of comparative experiments, has many 

 difficulties. 



Among the various methods which I have myself tried, I believe 

 the following may be recommended as the most practicable in 

 the generality of cases, and as applicable not only to the purpose 

 of ascertaining the consistence of mixed earths, but also that of 

 the clays, and even of very strong mortars. 



We take the earths we wish to compare in a moderately and 

 uniformly moistened state, and having prepared an open mould 

 or socket of wood (or better of metal), open at the top and bot- 

 tom, w^e form oblong square -cornered pieces (or little bricks) 



one -third of an inch in breadth and thickness, and about two 

 inches long ; we either leave these in the mould to dry of them- 

 selves, or remove them from it while in their fresh damp state (by 

 the contrary pressure of a piece of wood of equal size and form) ; 

 we then allow this moulded earth to dry first in the air and shade, 

 and afterwards to become perfectly dried at a higher tempe- 

 rature of about 144 J*' F. The different degrees of firmness of 

 the dried earths may now be more easily ascertained by the 

 following simple instrument : — 



* See the sketch of this in the ' Flora of the Kingdom of Hanover,' p. 307, 

 Gbttingen, 1822. 



